Influence of injection parameters on the final surface quality of Al-Si-Cu die cast components

Abstract

In foundry practice the occurrence of solidification
defects limits the production and the performance of cast
components. In high-pressure die casting (HPDC) the
most common defects are shrinkage or gas porosities
and bifilms.
Thin sections, typical of HPDC components, are the most
susceptible to casting defects, and these microstructural
imperfections can be detrimental to both the mechanical
and aesthetic properties. Even though laminations are
not as harmful as internal defects, die cast components
with this kind of superficial defects are always rejected by
customers, thus requiring further machining operations.
The aim of this study is to analyse the lamination defects
that occur on the surface of some Al-Si-Cu cast covers
produced by means of HPDC. In order to evaluate the
influence of the different injection parameters on the final
quality of the die casting products, melt temperature,
plunger speed and upset pressure have been varied
within a range of suitable values. The obtained castings
have been studied by performing visual inspections and
metallographic analyses by means of optical microscopy
(OM), revealing the presence of many bifilms spread over
the entire cross section of some cast parts.
The presence of laminations, bifilms and cold shuts has
been correlated to the considered processing conditions,
proposing a new criterion parameter for the quantification
of surface quality, called Lamination Ratio (LR).